In a scroll compressor, an orbiting scroll that performs an orbit movement by a crank shaft is provided with an orbit wrap of an involute shape thereby to form a compression chamber that consecutively moves with a fixed wrap of an involute shape of a fixed scroll. As the orbiting scroll performs an eccentric orbit movement by a rotation of the crank shaft, a volume of the compression chamber is decreased thereby to compress a refrigerant contained in the compression chamber. When the scroll compressor is operated with a certain compression ratio, the compressed refrigerant is discharged through an outlet.
The scroll compressor can implement a relatively higher compression ratio than any other compressor, and can generate a stable torque by smoothly performing a suction stroke, a compression stroke, and a discharge stroke of a refrigerant. Accordingly, the scroll compressor is being widely used to compress a refrigerant in an air conditioner, etc. When the scroll compressor is normally driven, a suction chamber of a low pressure and a discharge chamber of a high pressure are divided from each other. On the contrary, when the scroll compressor is abnormally driven in a state of a low suction pressure such as a pump down or a cycle clogging, a refrigerant of a high pressure discharged to the discharge chamber is introduced into a compression chamber through the suction chamber under a state that the suction chamber is connected to the discharge chamber, thereby preventing a high vacuum state of the compressor.
FIG. 1 is a sectional view showing an example of a scroll compressor having a vacuum preventing apparatus in accordance with the conventional art, FIG. 2 is a sectional view showing an operation state of the vacuum preventing apparatus when the scroll compressor is normally driven in accordance with the conventional art, and FIG. 3 is a sectional view showing an operation state of the vacuum preventing apparatus when the scroll compressor is driven at a high vacuum state in accordance with the conventional art.
As shown, the conventional scroll compressor comprises a casing 10 divided into a suction chamber S1 of a low pressure and a discharge chamber S2 of a high pressure; a main frame 20 fixedly installed in the casing 10; a fixed scroll 30 fixedly installed at an upper surface of the main frame 20 and having a compression chamber P that consecutively moves with an orbiting scroll 40; and a vacuum preventing unit 50 installed at the fixed scroll 30 for introducing a discharged refrigerant to the compression chamber P by connecting the discharge chamber S2 of a high pressure to the suction chamber S1 of a low pressure when a pressure of the compression chamber P is lowered into a pressure less than a certain pressure.
The casing 10 is divided into the suction chamber S1 of a low pressure and the discharge chamber S2 of a high pressure by a high-low pressure separation plate 11 of which an inner circumferential surface is adhered to an upper surface of a plate 31 of the fixed scroll 30 and an outer circumferential surface thereof is adhered to an inner circumferential surface of the casing 10. A suction pipe 12 is connected to the suction chamber S1, and a discharge pipe 13 is connected to the discharge chamber S2.
A bypass channel for opening and closing the suction chamber S1 and the discharge chamber S2 of the casing 10 by a sliding valve 51 of the vacuum preventing unit 50 is formed at the plate 31 of the fixed scroll 30. The bypass channel comprises a valve hole 32 concaved with a certain depth at the plate 31 of the fixed scroll 30 in a horizontal direcrion-4, a suction pressure channel 33 through which the valve hole 32 is connected to the suction chamber S2 of the casing 10, a middle pressure channel 34 through which the valve hole 32 is connected to the compression chamber, and a discharge pressure channel 35 through which the valve hole 32 is connected to the discharge chamber S2 of the casing 10.
The vacuum preventing unit 50 comprises a sliding valve 51 for closing the discharge pressure channel 35 by being slidably inserted into the valve hole 32 in a horizontal direction when the compression chamber P maintains a certain pressure, and for introducing a refrigerant inside the discharge chamber S2 into the suction chamber S1 by connecting the discharge pressure channel 35 to the suction pressure channel 33 when a pressure of the compression chamber P is lowered into a pressure less than the certain pressure; and a valve spring 52 provided at one side of the sliding valve 51 for elastically supporting the sliding valve 51.
Unexplained reference numeral 36 denotes a fixed wrap, 37 denotes an inlet, 38 denotes an outlet, 41 denotes an orbit wrap, 53 denotes a valve cover, 54 denotes a fixing pin, 61 denotes a stator, 62 denotes a rotor, 63 denotes a crank shaft, and 64 denotes a sub frame.
In the conventional vacuum preventing apparatus of a scroll compressor, when a new refrigerant is supplied to the compression chamber P, the vacuum preventing unit 50 closes between the discharge pressure channel 35 of the fixed scroll 30 and the suction pressure channel 33 and thus a refrigerant is normally compressed. On the contrary, when a little amount of refrigerant is sucked into the compression chamber P, the vacuum preventing unit 50 connects the discharge pressure channel 35 to the suction pressure channel 33 so that a refrigerant discharged to the discharge chamber S2 can be supplied to the compression chamber P via the suction chamber S1.
As shown in FIG. 2, when the compression chamber P maintains a certain pressure, the pressure of the compression chamber P becomes equivalent to a resultant force between an elastic force of the valve spring 52 and a pressure of the suction chamber S1, and thus the sliding valve 51 closes the discharge pressure channel 35. On the contrary, as shown in FIG. 3, when the pressure of the compression chamber P is lowered into a pressure less than the certain pressure, the pressure of the compression chamber P becomes smaller than the resultant force between an elastic force OT the valve spring 52 and a pressure of the suction chamber S1. As the result, the sliding valve 51 is moved towards an opposite side to the valve spring 52, and thus the discharge pressure channel 35 is connected to the suction pressure channel 33.
However, the conventional vacuum preventing apparatus of a scroll compressor has the following problems.
First, the valve hole 32 is concaved by a certain depth at an outer circumferential surface of the plate 31 of the fixed scroll 30 towards a center of the plate 31, and the middle pressure channel 34 or the discharge pressure channel 35 is connected to the valve hole 32. As the result, burr generated when the middle pressure channel 34 and the discharge pressure channel 35 are mechanically processed remains in the valve hole 32 thereby to serve as an obstacle when the sliding valve 51 is operated.
Second, oil and refrigerant inside the compression chamber P are introduced into the valve hole 32 through the middle pressure channel 34 connected to the valve hole 32, and then remain in the valve hole 32 thereby to serve as an obstacle when the sliding valve 51 is operated.
Third, since the valve hole 32 is formed at a lateral wall of the fixed scroll 30 in a horizontal direction, a processing of the valve hole 32 is difficult, a defective proportion in processing the fixed scroll 30 is increased, and thus a production cost for the fixed scroll 30 is increased. Furthermore, since a gap between the valve hole 32 and the sliding valve 51 is increased due to an inaccurate dimension of the valve hole 32, a refrigerant inside the discharge chamber S2 is leaked thereby to degrade an efficiency of the compressor.